title: Cation-induced kinetic trapping and enhanced hydrogen adsorption in a modulated anionic metal-organic framework.
abstract: Metal-organic frameworks (MOFs)--microporous materials constructed by bridging metal centres with organic ligands--show promise for applications in hydrogen storage, which is a key challenge in the development of the 'hydrogen economy'. Their adsorption capacities, however, have remained insufficient for practical applications, and thus strategies to enhance hydrogen-MOF interactions are required. Here we describe an anionic MOF material built from In(III) centres and tetracarboxylic acid ligands (H(4)L) in which kinetic trapping behaviour--where hydrogen is adsorbed at high pressures but not released immediately on lowering the pressure--is modulated by guest cations. With piperazinium dications in its pores, the framework exhibits hysteretic hydrogen adsorption. On exchange of these dications with lithium cations, no hysteresis is seen, but instead there is an enhanced adsorption capacity coupled to an increase in the isosteric heat of adsorption. This is rationalized by the different locations of the cations within the pores, determined with precision by X-ray crystallography.
authors.affiliation: School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
authors.forename: Sihai
authors.initials: S
authors.lastname: Yang
authors.forename: Xiang
authors.initials: X
authors.lastname: Lin
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Blake
authors.forename: Gavin S
authors.initials: GS
authors.lastname: Walker
authors.forename: Peter
authors.initials: P
authors.lastname: Hubberstey
authors.forename: Neil R
authors.initials: NR
authors.lastname: Champness
authors.forename: Martin
authors.initials: M
authors.lastname: Schröder
mesh_terms: D000327:Adsorption; D000838:Anions / Q000737:chemistry; D002264:Carboxylic Acids / Q000138:chemical synthesis / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D018360:Crystallography, X-Ray; D006859:Hydrogen / Q000737:chemistry*; D007204:Indium / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D016062:Porosity; D013499:Surface Properties
chemical_list: D000838:Anions; D002264:Carboxylic Acids; D002412:Cations; D008024:Ligands; D009942:Organometallic Compounds; D007204:Indium; D006859:Hydrogen